Ravichandran R, Binukumar J P, Davis C A, Krishnamurthy K, Sivakumar S S
Medical Physics Unit, Department of Radiation Oncology, National Oncology Center, The Royal Hospital, Oman.
J Med Phys. 2007 Jul;32(3):92-6. doi: 10.4103/0971-6203.35720.
There is need for simple methods for checking consistency of beam outputs and energy in linear accelerators used for radiotherapy. A method was designed by the department using perspex phantom with which the dosimetric data of two medical linear accelerators (Clinac 600 CD, Clinac 2300 CD) were evaluated over a period of 30 months. The efficacy of methods followed was checked. Routine beam consistency checks were designed for photon beams with 15 cm/ 5 cm depth ionizations in perspex phantom and variable depth combinations for electron beams. Calculated ionization ratios were compared with measured values to show their significance. The dose/MU for all radiation beams was maintained within 2% accuracy over the period of 30 months. Clinac 600 CD machine showed decreasing trend of cGy/MU, while Clinac 2300 CD showed increasing trend of cGy/MU over a period, which needed tuning of monitor chamber two times each. Tuning of output to achieve standard value was carried out once, for all electron energies when the output dose/MU exceeded 3%. During one week (June 2005), there were slight changes in electron energy detected using the ratio method, which did not recur anytime afterwards. The methods designed are adequate to find the consistency in the beam output and energies in the radiotherapy linacs.
需要有简单的方法来检查用于放射治疗的直线加速器中射束输出和能量的一致性。该部门设计了一种方法，使用有机玻璃模体，在30个月的时间里评估了两台医用直线加速器（Clinac 600 CD、Clinac 2300 CD）的剂量学数据。检查了所采用方法的有效性。针对有机玻璃模体中15厘米/5厘米深度电离的光子束以及电子束的可变深度组合，设计了常规射束一致性检查。将计算出的电离比与测量值进行比较以显示其意义。在30个月的时间里，所有辐射束的剂量/监测单位（MU）保持在2%的精度范围内。Clinac 600 CD机器显示出cGy/MU呈下降趋势，而Clinac 2300 CD在一段时间内显示出cGy/MU呈上升趋势，这两台机器各自需要对监测电离室进行两次调整。当输出剂量/MU超过3%时，针对所有电子能量对输出进行一次调整以达到标准值。在一周（2005年6月）期间，使用比率法检测到电子能量有轻微变化，之后未再出现过。所设计的方法足以发现放射治疗直线加速器中射束输出和能量的一致性。
